The Organization of Collective Group Movements in Wild Barbary Macaques (Macaca sylvanus): Social Structure Drives Processes of Group Coordination in Macaques

Abstract

Social animals have to coordinate activities and collective movements to benefit from the advantages of group living. Animals in large groups maintain cohesion by self-organization processes whereas in smaller groups consensus decisions can be reached. Where consensus decisions are relevant leadership may emerge. Variation in the organization of collective movements has been linked to variation in female social tolerance among macaque species ranging from despotic to egalitarian. Here we investigated the processes underlying group movements in a wild macaque species characterized by a degree of social tolerance intermediate to previously studied congeneric species. We focused on processes before, during and after the departure of the first individual. To this end, we observed one group of wild Barbary macaques (Macaca sylvanus) in the Middle Atlas, Morocco using all-occurrence behaviour sampling of 199 collective movements. We found that initiators of a collective movement usually chose the direction in which more individuals displayed pre-departure behavior. Dominant individuals contributed to group movements more than subordinates, especially juveniles, measured as frequencies of successful initiations and pre-departure behaviour. Joining was determined by affiliative relationships and the number of individuals that already joined the movement (mimetism). Thus, in our study group partially shared consensus decisions mediated by selective mimetism seemed to be prevalent, overall supporting the suggestion that a species’ social style affects the organization of group movements. As only the most tolerant species show equally shared consensus decisions whereas in others the decision is partially shared with a bias to dominant individuals the type of consensus decisions seems to follow a stepwise relation. Joining order may also follow a stepwise, however opposite, relationship, because dominance only determined joining in highly despotic, but not in intermediate and tolerant species.

Recruitment and monitoring behaviors by leaders predict following in wild Barbary macaques (<i>Macaca sylvanus</i>)

“…Confirming the findings of our previous study and like in Tonkean macaques, we found that the success of an individ- ual's attempts to initiate a collective movement is not predicted by dominance rank, but by social integration if including juveniles in the analyses (Sueur and Petit, 2008a;Seltmann et al, 2013). In rhesus macaques (M. mulatta), both social integration and a high dominance rank favored a positive outcome of an initiation movement (Sueur and Petit, 2008a).…”

“…In our former analyses, we focused on the individual characteristics of predeparture displaying individuals and initiators of collective movements. We found that adult, high-ranking (male) group members had a disproportionately strong influence on collective movements (Seltmann et al, 2013).…”

“…To exactly define group movement related terms, we conducted a 2-week pilot study as suggested by Pyritz et al (2010) for this social group of Barbary macaques. Details of the pilot study have been described elsewhere (Seltmann et al, 2013) and yielded the following definitions:…”

“…By combining the three parameters measuring body contact and interindividual distance (within 1.5 or 5 m; see above), we estimated the centrality of individuals in the social network as their composite index of social integration (CIS). This was done similar to Sapolsky et al (1997) and Silk et al (2003) as follows:…”

“…In a previous study on group movements in wild Barbary macaques we observed potential communication behaviors, but we did not evaluate the role of these behaviors in determining group movements (Seltmann et al, 2013). We have previously established that decisions about the timing and direction of group movements are partially shared consensus decisions.…”